Inkjet ink composition and an ink/receiver combination

ABSTRACT

An aqueous inkjet ink including: a pigment; a water-soluble heat sensitive ionomer; at least one surfactant; and a humectant; wherein the ionomer is a charged polymer having at least 15 mole % of the recurring units negatively or positively charged.

CROSS REFERENCE TO RELATED APPLICATIONS

This application relates to commonly assigned copending application Ser.No. 10/256,519, entitled AN AQUEOUS INKJET INK AND RECEIVER COMBINATION;application Ser. No. 10/256,822, entitled INKJET PRINTING METHOD FOR ANINK/RECEIVER COMBINATION; application Ser. No. 10/256,589, entitledINKJET PRINTING METHOD; application Ser. No. 10/256,989entitled INK JETINK COMPOSITION AND INK/RECEIVER COMBINATION; application Ser. No.10/083,258, entitled IMAGING MEMBERS CONTAINING CARBON BLACK AND METHODSOF IMAGING AND PRINTING.

FIELD OF THE INVENTION

This invention relates to an aqueous ink jet ink composition comprisingpigment and a heat sensitive ionomer and to a combination of the ink anda receiver.

BACKGROUND OF THE INVENTION

Ink jet printing is a non-impact method for producing images by thedeposition of ink droplets on a substrate (paper, transparent film,fabric, etc.) in response to digital signals. Ink jet printers havefound broad applications across markets ranging from industrial labelingto short run printing to desktop document and pictorial imaging andlarge format printing for outdoor applications such as banners,signages, displays, posters, billboard and bus wraps.

This technique of printing is well suited for printing on a variety ofsurfaces (receivers) including porous and non-porous surfaces. Porousinkjet receivers have the advantage of large fluid intake and thisprovides fast printing speed. However, in some applications, such asbanners, signages, displays, posters, billboard and bus wraps, theseporous receivers suffer from durability issues such as lightfastness,waterfastness, abrasion resistance and weather resistance. In order toovercome these problems, the prints are usually post treated by methodssuch as lamination, which adds to the cost considerably. Historically,in order to overcome these problems, solvent based inks or UV curableinks were developed to be printed on non-absorbing substrates such asvinyl to achieve the desired durability. U.S. Pat. No.4,106,027describes such a solvent based ink that is suitable forprinting images on non-absorbing surfaces with improved adhesion anddurability. EP 0 882 104 B1 describes a UV curable inkjet inkcomposition for better durability of the print on non-absorbingsubstrate. A significant environmental, health and safety concern withboth of these types of ink is the evaporation of solvent or UV monomerduring printing.

U.S. Pat. No. 6,087,416 describes the use of an aqueous based pigmentink for printing on non-absorbing vinyl substrate. That ink contains agrafted copolymer binder that is soluble in the aqueous vehicle butinsoluble in water. However, the problem with the ink is that, due tothe soluble nature of the binder in the ink vehicle, the ink viscosityis high and the printing reliability is poor. In addition, the printedimages are not durable to solvent.

U.S. Pat. No. 4,762,875 describes a printing ink containing pigment andpolymer additives for plastics and metal surfaces, however, there is aproblem with this invention that the solid content for this ink is high,therefore the viscosity of the ink is too high for inkjet inkapplications; in addition, the additives used in this invention ishydrophilic in nature therefore the resulted coatings has poor waterresistance.

JP 01262022A discloses an ink jet ink composition containing pigment anda thermal curing agent. There is a problem with this invention in thatthere are excess of the hydrophilic components remaining in the print,an extra step of “washing” has to be done to remove these materials inorder to achieve the image durability.

U.S. patent application Ser. No. 10/083,258 discloses the use of acomposition containing a heat sensitive polymer in printing plateapplications; However, no use in ink jet inks is disclosed.

Therefore, there is a need for an aqueous based ink jet ink thatprovides good waterfastness, lightfastness, abrasion resistance, goodadhesion to non-absorbing substrates including untreated vinyl, and thatcan be printed reliably through a piezo or thermal printhead.

SUMMARY OF THE INVENTION

This and other objects are achieved in accordance with the presentinvention which discloses an aqueous inkjet ink comprising:

-   -   a pigment;    -   a heat-sensitive ionomer,    -   at least one surfactant;    -   a humectant;    -   wherein the ionomer is a charged polymer having at least 5 mole        % of the recurring units negatively or positively charged.

Another embodiment of the invention discloses:

An aqueous inkjet ink and receiver combination wherein the aqueousinkjet ink comprises:

-   -   a pigment;    -   a heat sensitive ionomer;    -   at least one surfactant;    -   a humectant; and        the receiver comprises a non-absorbing substrate.

It was found that the colloid stability, stain resistance and abrasionresistance of an ink jet image was improved using the compositiondescribed herein.

DETAILED DESCRIPTION OF THE INVENTION

The ink composition of the present invention is suited for printing on avariety of substrates, especially on non-absorbing substrates. Thenon-absorbing substrates that may be used in the present inventioninclude any substrate that is essentially non-porous. They are usuallynot specially treated for additional liquid absorption. Therefore, thesematerials have very low or no liquid absorbing capacity. Examples ofsuch non-absorbing substrates are metals such as aluminum, copper,stainless steel and alloy etc.; plastics such as vinyl, polycarbonate,polytetrafluoroethylene (PTFE), polyethylene, polypropylene,polystyrene, cellulose; and other substrates such as ceramics, glass.

In order to achieve good image durability when printing aqueous basedinks onto a non-absorbing substrate, the polymeric binder in the inkcomposition needs to be essentially hydrophobic, capable of providinggood adhesion strength to the non-absorbing substrate, and also not beeasily re-dispersible in water after drying. In addition, good inkstorage stability as well as nozzle jettability requires the hydrophobicpolymer binder to be both sufficiently stable as a dispersion and becompatible with other ink components, such as surfactant, colorants andhumectants. Furthermore, the ink should have sufficiently low surfacetension to have good wettability when printing unto a non-absorbingsubstrate.

The pigment used in the current invention can be either self-dispersiblepigment such as those described in U.S. Pat. No. 5,630,868, encapsulatedpigments as those described in the pending U.S. patent application Ser.No. 09/822,723, or can be stabilized by a dispersant. The process ofpreparing inks from pigments commonly involves two steps: (a) adispersing or milling step to break up the pigment to the primaryparticle, and (b) dilution step in which the dispersed pigmentconcentrate is diluted with a carrier and other addenda to a workingstrength ink. In the milling step, the pigment is usually suspended in acarrier (typically the same carrier as that in the finished ink) alongwith rigid, inert milling media. Mechanical energy is supplied to thispigment dispersion, and the collisions between the milling media and thepigment cause the pigment to deaggregate into its primary particles. Adispersant or stabilizer, or both, is commonly added to the pigmentdispersion to facilitate the deaggregation of the raw pigment, tomaintain colloidal particle stability, and to retard particlereagglomeration and settling.

There are many different types of materials which may be used as millingmedia, such as glasses, ceramics, metals, and plastics. In a preferredembodiment, the grinding media can comprise particles, preferablysubstantially spherical in shape, e.g., beads, consisting essentially ofa polymeric resin. In general, polymeric resins suitable for use asmilling media are chemically and physically inert, substantially free ofmetals, solvent and monomers, and of sufficient hardness and firabilityto enable them to avoid being chipped or crushed during milling.Suitable polymeric resins include crosslinked polystyrenes, such aspolystyrene crosslinked with divinylbenzene, styrene copolymers,polyacrylates such as poly(methyl methylacrylate), polycarbonates,polyacetals, such as Derlin™, vinyl chloride polymers and copolymers,polyurethanes, polyamides, poly(tetrafluoroethylenes), e.g., Teflon™,and other fluoropolymers, high density polyethylenes, polypropylenes,cellulose ethers and esters such as cellulose acetate,poly(hydroxyethylmethacrylate), poly(hydroxyethylacrylate), siliconecontaining polymers such as polysiloxanes and the like. The polymer canbe biodegradable. Exemplary biodegradable polymers includepoly(lactides), poly(glycolids) copolymers of lactides and glycolide,polyanhydrides, poly(imino carbonates), poly(N-acylhydroxyproline)esters, poly(N-palmitoyl hydroxyprolino) esters, ethylene-vinyl acetatecopolymers, poly(orthoesters), poly(caprolactones), andpoly(phosphazenes). The polymeric resin can have a density from 0.9 to3.0 g/cm3. Higher density resins are preferred inasmuch as it isbelieved that these provide more efficient particle size reduction. Mostpreferred are crosslinked or uncrosslinked polymeric media based onstyrene.

Milling can take place in any suitable grinding mill. Suitable millsinclude an air jet mill, a roller mill, a ball mill, an attritor milland a bead mill. A high speed mill is preferred. By high speed mill wemean milling devices capable of accelerating milling media to velocitiesgreater than about 5 meters per second. Sufficient milling mediavelocity is achieved, for example, in Cowles-type saw tooth impellerhaving a diameter of 40 mm when operated at 9,000 rpm. The preferredproportions of the milling media, the pigment, the liquid dispersionmedium and dispersant can vary within wide limits and depends, forexample, up on the particular material selected and the size and densityof the milling media etc. After milling is complete, the dispersion ofactive material is separated from the grinding media by simple sievingor filtration. With either of the above modes the preferred amounts andratios of the ingredients of the mill grind will vary widely dependingupon the specific materials and the intended applications. The contentsof the milling mixture comprise the mill grind and the milling media.The mill grind comprises pigment, dispersant and a liquid carrier suchas water. For aqueous ink jet inks, the pigment is usually present inthe mill grind at 1 to 50 weight %, excluding the milling media. Theweight ratio of pigment to dispersant is 20:1 to 1:2. The high speedmill is a high agitation device, such as those manufactured byMorehouse-Cowles, Hockmeyer et al.

The dispersant is another ingredient in the mill grind. It can be eithera small molecule or a polymer. Preferred dispersants used in the presentinvention include sodium dodecyl sulfate, acrylic and styrene-acryliccopolymers, such as those disclosed in U.S. Pat. Nos. 5,085,698 and5,172,133, and sulfonated polyesters and styrenics, such as thosedisclosed in U.S. Pat. No. 4,597,794. Other patents referred to above inconnection with pigment availability also disclose a wide variety ofdispersants. The dispersant used in the examples is potassiumN-methyl-N-oleoyl taurate (K-OMT).

The milling time can vary widely and depends upon the pigment,mechanical means and residence conditions selected, the initial anddesired final particle size, etc. For aqueous mill grinds using thepreferred pigments, dispersants, and milling media described above,milling times will typically range from 1 to 100 hours. The milledpigment concentrate is preferably separated from the milling media byfiltration.

The pigment particles useful in the invention may have any particlesizes which can be jetted through a print head. Preferably, the pigmentparticles have a mean particle size of less than about 0.5 micron, morepreferably less than about 0.2 micron.

A wide variety of organic and inorganic pigments, alone or incombination, may be selected for use in the present invention. Colorantparticles which may be used in the invention include pigments asdisclosed, for example in U.S. Pat. Nos. 5,026,427; 5,086,698;5,141,556; 5,160,370; and 5,169,436, the disclosures of which are herebyincorporated by reference. The exact choice of pigments will depend uponthe specific application and performance requirements such as colorreproduction and image stability. Pigments suitable for use in thepresent invention include, for example, azo pigments, monoazo pigments,disazo pigments, azo pigment lakes, β-Naphthol pigments, Naphthol ASpigments, benzimidazolone pigments, disazo condensation pigments, metalcomplex pigments, isoindolinone and isoindoline pigments, polycyclicpigments, phthalocyanine pigments, quinacridone pigments, perylene andperinone pigments, thioindigo pigments, anthrapyrimidone pigments,flavanthrone pigments, anthanthrone pigments, dioxazine pigments,triarylcarbonium pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, titanium oxide, iron oxide, and carbon black. Typicalexamples of pigments which may be used include Color Index (C. I.)Pigment Yellow 1, 2, 3, 5, 6, 10, 12, 13, 14, 16, 17, 62, 65, 73, 74,75, 81, 83, 87, 90, 93, 94, 95, 97, 98, 99, 100, 101, 104, 106, 108,109, 110, 111, 113, 114, 116, 117, 120, 121, 123, 124, 126, 127, 128,129, 130, 133, 136, 138, 139, 147, 148, 150, 151, 152, 153, 154, 155,165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 179,180, 181, 182, 183, 184, 185, 187, 188, 190, 191, 192, 193, 194; C. I.Pigment Orange 1, 2, 5, 6, 13, 15, 16, 17, 17:1, 19, 22, 24, 31, 34, 36,38, 40, 43, 44, 46, 48, 49, 51, 59, 60, 61, 62, 64, 65, 66, 67, 68, 69;C. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,17, 18, 21, 22, 23, 31, 32, 38, 48:1, 48:2, 48:3, 48:4, 49:1, 49:2,49:3, 50:1, 51, 52:1, 52:2, 53:1, 57:1, 60:1, 63:1, 66, 67, 68, 81, 95,112, 114, 119, 122, 136, 144, 146, 147, 148, 149, 150, 151, 164, 166,168, 169, 170, 171, 172, 175, 176, 177, 178, 179, 181, 184, 185, 187,188, 190, 192, 194, 200, 202, 204, 206, 207, 210, 211, 212, 213, 214,216, 220, 222, 237, 238, 239, 240, 242, 243, 245, 247, 248, 251, 252,253, 254, 255, 256, 258, 261, 264; C.I. Pigment Violet 1, 2, 3, 5:1, 13,19, 23, 25, 27, 29, 31, 32, 37, 39, 42, 44, 50; C.I. Pigment Blue 1, 2,9, 10, 14, 15:1, 15:2, 15:3, 15:4, 15:6, 15, 16, 18, 19, 24:1, 25, 56,60, 61, 62, 63, 64, 66; C.I. Pigment Green 1, 2, 4, 7, 8, 10, 36, 45;C.I. Pigment Black 1, 7, 20, 31, 32, and C.I. Pigment Brown 1, 5, 22,23, 25, 38, 41, 42. In a preferred embodiment of the invention, thepigment is C.I. Pigment Blue 15:3, C.I. Pigment Red 122, C.I. PigmentYellow 155, C.I. Pigment Yellow 74, C.I. Pigment Black 7 orbis(phthalocyanylalumino)tetraphenyldisiloxane as described in U.S. Pat.No. 4,311,775, the contents of which are incorporated herein byreference.

In the case of organic pigments, the ink may contain up to approximately20% pigment by weight, but will generally be in the range ofapproximately 0.1 to 10%, preferably approximately 0.1 to 5%, by weightof the total ink composition for most ink jet printing applications. Ifan inorganic pigment is selected, the ink will tend to contain higherweight percentages of pigment than with comparable inks employingorganic pigments.

Instead of pigment, a dye can also be used in the current invention.Preferably, the dye is a water insoluble dye. To make the ink, the waterinsoluble dye can be dispersed or encapsulated into water dispersibleparticles as disclosed in U.S. Ser. No. 10/020,694, filed Dec. 14, 2001.A broad range of water-insoluble dyes may be used in the invention suchas an oil dye, a disperse dye, or a solvent dye, such as Ciba-GeigyOrasol Red G, Ciba-Geigy Orasol Blue GN, Ciba-Geigy Orasol Pink, andCiba-Geigy Orasol Yellow. Preferred water-insoluble dyes can be xanthenedyes, methine dyes, polymethine dyes, anthroquinone dyes, merocyaninedyes, azamethine dyes, azine dyes, quinophthalone dyes, thiazine dyes,oxazine dyes, phthalocyanine dyes, mono or poly azo dyes, and metalcomplex dyes. More preferably, the water insoluble dyes can be an azodye such as a water insoluble analog of the pyrazoleazoindole dyedisclosed in U.S. Ser. No. 09/689,184 filed Oct. 12, 2000, incorporatedherein by reference, and the arylazoisotbiazole dye disclosed in U.S.Pat. No. 4,698,651, incorporated herein by reference, or a metal-complexdye, such as the water-insoluble analogues of the dyes described in U.S.Pat. Nos. 5,997,622 and 6,001,161, both incorporated herein byreference, i.e., a transition metal complex of an8-heterocyclylazo-5-hydroxyquinoline. The solubility of the waterinsoluble dye used in the present invention should be less than 1 g/L inwater, and more preferably less than 0.5 g/L in water.

The water insoluble dye can be present in any effective amount in theink of the present invention, usually up to about 20% by weight of anink jet ink composition, and preferably from about 0.05 to 15 wt. %. Thecolorant used in the current invention can also be a dye. In a preferredembodiment of the invention, the dye is a water insoluble dye. To makethe ink, the water insoluble dye can be dispersed or encapsulated intowater dispersible particles as disclosed in Ser. No. 10/020,694, filedDec. 14, 2001. A broad range of water-insoluble dyes may be used in theinvention such as an oil dye, a disperse dye, or a solvent dye, such asCiba-Geigy Orasol Red G, Ciba-Geigy Orasol Blue GN, Ciba-Geigy OrasolPink, and Ciba-Geigy Orasol Yellow. Preferred water-insoluble dyes canbe xanthene dyes, methine dyes, polymethine dyes, anthroquinone dyes,merocyanine dyes, azamethine dyes, azine dyes, quinophthalone dyes,thiazine dyes, oxazine dyes, phthalocyanine dyes, mono or poly azo dyes,and metal complex dyes. More preferably, the water insoluble dyes can bean azo dye such as a water insoluble analog of the pyrazoleazoindole dyedisclosed U.S. Pat. No. 6,468,338, incorporated herein by reference, andthe arylazoisothiazole dye disclosed in U.S. Pat. No. 4,698,651,incorporated herein by reference, or a metal-complex dye, such as thewater-insoluble analogues of the dyes described in U.S. Pat. Nos.5,997,622 and 6,001,161, both incorporated herein by reference, i.e., atransition metal complex of an 8-heterocyclylazo-5-hydroxyquinoline. Thesolubility of the water insoluble dye used in the present inventionshould be less than 1 g/L in water, and more preferably less than 0.5g/L in water.

The water insoluble dye can be present in any effective amount in theink of the present invention, usually up to about 20% by weight of anink jet ink composition, and preferably from about 0.05 to 15 wt. %.

The heat sensitive ionomers used in the current invention are generallycomprised of recurring units, of which at least 5 mol % include ionicgroups of the same charge. Preferably, at least 15 mol % of therecurring groups include ionic groups of the same ionic charge. Thuseach of these polymers has a net positive or negative charge provided bythese ionic groups.

Representative ionomers useful in the practice of this invention can beselected from one or more of four broad classes of materials:

-   -   I) crosslinked or uncrosslinked vinyl polymers comprising        recurring units comprising positively-charged, pendant        N-alkylated aromatic heterocyclic groups,    -   II) crosslinked or uncrosslinked polymers comprising recurring        organoonium groups,    -   III) polymers comprising a pendant thiosulfate (Bunte salt)        group,    -   IV) polymers comprising recurring units comprising carboxy or        carboxylate groups.

Each class of ionomers is described in turn. The inkjet inks cancomprise one or more mixtures of ionomers from each class, or a mixtureof one or more ionomers of two or more classes as long as the mixedionomers are compatible with each other.

Class I Ionomers:

The Class I ionomers generally have a molecular weight of at least 1000and can be any of a wide variety of vinyl homopolymers and copolymershaving the requisite positively-charged groups. They are prepared fromethylenically unsaturated polymerizable monomers using any conventionalpolymerization technique. Preferably, the polymers are copolymersprepared from two or more ethylenically unsaturated polymerizablemonomers, at least one of which contains the desired pendantpositively-charged group, and another monomer that is capable ofproviding other properties, such as crosslinking sites and possiblyadhesion to the support. Procedures and reactants needed to preparethese polymers are well known. With the additional teaching providedherein, the known polymer reactants and conditions can be modified byone skilled in the art to attach a suitable cationic group.

The presence of a cationic group apparently provides or facilitates the“switching” of the printed layer from hydrophilic to hydrophobic in theareas that have been exposed to heat in some manner, when the cationicgroup reacts with its counterion. The net result is the loss of charge.Such reactions are more easily accomplished when the anion is morenucleophilic and/or more basic. For example, an acetate anion istypically more reactive than a chloride anion. By varying the chemicalnature of the anion, the reactivity of the heat-sensitive polymer can bemodified to provide optimal image resolution for a given set ofconditions (for example, laser hardware and power, and printing pressneeds) balanced with sufficient ambient shelf life. Useful anionsinclude the halides, carboxylates, sulfates, borates and sulfonates.Representative anions include, but are not limited to, chloride,bromide, fluoride, acetate, tetrafluoroborate, formate, sulfate,p-toluenesulfonate and others readily apparent to one skilled in theart. The halides and carboxylates are preferred.

The aromatic cationic group is present in sufficient recurring units ofthe polymer so that the heat-activated reaction described above canprovide desired hydrophobicity of the imaged printing layer. The groupscan be attached along a principal backbone of the polymer, or to one ormore branches of a polymeric network, or both. The aromatic groupsgenerally comprise 5 to 10 carbon, nitrogen, sulfur or oxygen atoms inthe ring (at least one being a positively-charged nitrogen atom), towhich is attached a branched or unbranched, substituted or unsubstitutedalkyl group. Thus, the recurring units containing the aromaticheterocyclic group can be represented by the following Structure I:

In this structure, R₁ is a branched or unbranched, substituted orunsubstituted alkyl group having from 1 to 12 carbon atoms (such asmethyl, ethyl, n-propyl, isopropyl, t-butyl, hexyl, methoxymethyl,benzyl, neopentyl and dodecyl). Preferably, R₁ is a substituted orunsubstituted, branched or unbranched alkyl group having from 1 to 6carbon atoms, and most preferably, it is substituted or unsubstitutedmethyl group.

R₂ can be a substituted or unsubstituted alkyl group (as defined above,and additionally a cyanoalkyl group, a hydroxyalkyl group or alkoxyalkylgroup), substituted or unsubstituted alkoxy having 1 to 6 carbon atoms(such as methoxy, ethoxy, isopropoxy, oxymethylmethoxy, n-propoxy andbutoxy), a substituted or unsubstituted aryl group having 6 to 14 carbonatoms in the ring (such as phenyl, naphthyl, anthryl, p-methoxyphenyl,xylyl, and alkoxycarbonylphenyl), halo (such as chloro and bromo), asubstituted or unsubstituted cycloalkyl group having 5 to 8 carbon atomsin the ring (such as cyclopentyl, cyclohexyl and 4-methylcyclohexyl), ora substituted or unsubstituted heterocyclic group having 5 to 8 atoms inthe ring including at least one nitrogen, sulfur or oxygen atom in thering (such as pyridyl, pyridinyl, tetrahydrofuranyl andtetrahydropyranyl). Preferably, R₂ is substituted or unsubstitutedmethyl or ethyl group.

Z″ represents the carbon and any additional nitrogen, oxygen, or sulfuratoms necessary to complete the 5- to 10-membered aromaticN-heterocyclic ring that is attached to the polymeric backbone. Thus,the ring can include two or more nitrogen atoms in the ring (forexample, N-alkylated diazinium or imidazolium groups), or N-alkylatednitrogen-containing fused ring systems including, but not limited to,pyridinium, quinolinium, isoquinolinium acridinium, phenanthradinium andothers readily apparent to one skilled in the art.

W⁻ is a suitable anion as described above. Most preferably it is acetateor chloride.

Also in Structure I, n is 0 to 6, and is preferably 0 or 1. Mostpreferably, n is 0.

The aromatic heterocyclic ring can be attached to the polymeric backboneat any position on the ring. Preferably, there are 5 or 6 atoms in thering, one or two of which are nitrogen. Thus, the N-alkylated nitrogencontaining aromatic group is preferably imidazolium or pyridinium andmost preferably it is imidazolium.

The recurring units containing the cationic aromatic heterocycle can beprovided by reacting a precursor polymer containing unalkylated nitrogencontaining heterocyclic units with an appropriate alkylating agent (suchas alkyl sulfonate esters, alkyl halides and other materials readilyapparent to one skilled in the art) using known procedures andconditions.

Preferred Class I ionomers can be represented by the following StructureII:

wherein X represents recurring units to which the N-alkylated nitrogencontaining aromatic heterocyclic groups (represented by HET⁺) areattached, Y represents recurring units derived from ethylenicallyunsaturated polymerizable monomers that may provide active sites forcrosslinking using any of various crosslinking mechanisms (describedbelow), W⁻ is a suitable anion as described above, and Z representsrecurring units derived from any additional ethylenically unsaturatedpolymerizable monomers. The various repeating units are present insuitable amounts, as represented by x being from about 15 to 100 mol %,y being from about 0 to about 20 mol %, and z being from 0 to 85 mol %.Preferably, x is from about 20 to about 98 mol %, y is from about 2 toabout 10 mol % and z is from 0 to about 70 mol %.

Crosslinking of the ionomers can be provided in a number of ways. Thereare numerous monomers and methods for crosslinking that are familiar toone skilled in the art. Some representative crosslinking strategiesinclude, but are not necessarily limited to:

-   -   a) reacting an amine or carboxylic acid or other Lewis basic        units with diepoxide crosslinkers,    -   b) reacting an epoxide units within the polymer with        difunctional amines, carboxylic acids, or other difunctional        Lewis basic unit,    -   c) irradiative or radical-initiated crosslinking of double        bond-containing units such as acrylates, methacrylates,        cinnamates, or vinyl groups,    -   d) reacting a multivalent metal salts with ligating groups        within the polymer (the reaction of zinc salts with carboxylic        acid-containing polymers is an example),    -   e) using crosslinkable monomers that react via the Knoevenagel        condensation reaction, such as (2-acetoacetoxy)ethyl acrylate        and methacrylate,    -   f) reacting an amine, thiol, or carboxylic acid groups with a        divinyl compound (such as bis (vinylsulfonyl) methane) via a        Michael addition reaction,    -   g) reacting a carboxylic acid units with crosslinkers having        multiple aziridine units,    -   h) reacting a crosslinkers having multiple isocyanate units with        amines, thiols, or alcohols within the polymer,    -   i) mechanisms involving the formation of interchain sol-gel        linkages [such as the use of the 3-(trimethoxysilyl)        propylmethacrylate monomer],    -   j) oxidative crosslinking using an added radical initiator (such        as a peroxide or hydroperoxide),    -   k) autooxidative crosslinking, such as employed by alkyd resins,    -   l) sulfur vulcanization, and    -   m) processes involving ionizing radiation.

Monomers having crosslinkable groups or active crosslinkable sites (orgroups that can serve as attachment points for crosslinking additives,such as epoxides) can be copolymerized with the other monomers notedabove. Such monomers include, but are not limited to,3-(trimethoxysilyl)propyl acrylate or methacrylate, cinnamoyl acrylateor methacrylate, N-methoxymethyl methacrylamide, N-aminopropylacrylamidehydrochloride, acrylic or methacrylic acid and hydroxyethylmethacrylate.

Additional monomers that provide the repeating units represented by “Z”in the Structure II above include any useful hydrophilic or oleophilicethylenically unsaturated polymerizable monomer that may provide desiredphysical or printing properties to the hydrophilic imaging layer. Suchmonomers include, but are not limited to, acrylates, methacrylates,isoprene, acrylonitrile, styrene and styrene derivatives, acrylamides,methacrylamides, acrylic or methacrylic acid and vinyl halides.

Representative Class I ionomers are identified below as Polymers 1, 3,4, and 6. Mixtures of these polymers can also be used. Polymers 2 and 5below are precursors to useful Class I ionomers. Further details ofthese ionomers and methods for their preparation are provided in U.S.Pat. No. 6,180,831.

Polymer 1: Poly (1-vinyl-3-methylimidazoliumchloride-co-N-(3-aminopropyl) methacrylamide hydrochloride),

Polymer 2: Poly(methyl methacrylate-co-4-vinylpyridine),

Polymer 3: Poly(methyl methacrylate-co-N-methyl-4-vinylpyridiniumformate),

Polymer 4: Poly(methyl methacrylate-co-N-butyl-4 vinylpyridiniumformate),

Polymer 5: Poly(methyl methacrylate-co-2-vinylpyridine), and

Polymer 6: Poly(methyl methacrylate-co-N-methyl-2-vinylpyridiniumformate).

Class II Ionomers

The Class II ionomers also generally have a molecular weight of at least1000. They can be any of a wide variety of vinyl or non-vinylhomopolymers and copolymers.

Non-vinyl ionomers of Class II include, but are not limited to,polyesters, polyamides, polyamide-esters, polyarylene oxides andderivatives thereof, polyurethanes, polyxylylenes and derivativesthereof, silicon-based sol gels (solsesquioxanes), polyamidoamines,polyimides, polysulfones, polysiloxanes, polyethers, poly(etherketones), poly(phenylene sulfide) ionomers, polysulfides andpolybenzimidazoles. Preferably, such non-vinyl polymers are siliconbased sol gels, polyarylene oxides, poly(phenylene sulfide) ionomers orpolyxylylenes, and most preferably, they are poly(phenylene sulfide)ionomers. Procedures and reactants needed to prepare all of these typesof polymers are well known. With the additional teaching providedherein, the known polymer reactants and conditions can be modified by askilled artisan to incorporate or attach a suitable cationic organooniummoiety.

Silicon-based sol gels useful in this invention can be prepared as acrosslinked polymeric matrix containing a silicon colloid derived fromdi-, tri- or tetraalkoxy silanes. These colloids are formed by methodsdescribed in U.S. Pat. No. 2,244,325 (Bird), U.S. Pat. No. 2,574,902(Bechtold et al.), and U.S. Pat. No. 2,597,872 (Iler). Stabledispersions of such colloids can be conveniently purchased fromcompanies such as the DuPont Company. A preferred sol-gel usesN-trimethoxysilylpropyl-N,N,N-trimethylammonium acetate both as thecrosslinking agent and as the polymer layer forming material.

The presence of an organoonium moiety that is chemically incorporatedinto the ionomer in some fashion apparently provides or facilitates the“switching” of the printed layer from hydrophilic to oleophilic in theheat exposed areas upon exposure to energy that provides or generatesheat, when the cationic moiety reacts with its counterion. The netresult is the loss of charge. Such reactions are more easilyaccomplished when the anion of the organoonium moiety is morenucleophilic and/or more basic, as described above for the Class Ipolymers.

The organoonium moiety within the polymer can be chosen from atrisubstituted sulfur moiety (organosulfonium), a tetrasubstitutednitrogen moiety (organoammonium), or a tetrasubstituted phosphorousmoiety (organophosphonium). The tetrasubstituted nitrogen(organoammonium) moieties are preferred. This moiety can be chemicallyattached to (that is, pendant) the polymer backbone, or incorporatedwithin the backbone in some fashion, along with the suitable counterion.In either embodiment, the organoonium moiety is present in sufficientrepeating units of the polymer (at least 15 mol %) so that theheat-activated reaction described above can occur to provide desiredhydrophobicity of the imaging layer. When chemically attached as apendant group, the organoonium moiety can be attached along a principalbackbone of the polymer, or to one or more branches of a polymericnetwork, or both. When chemically incorporated within the polymerbackbone, the moiety can be present in either cyclic or acyclic form,and can also form a branching point in a polymer network. Preferably,the organoonium moiety is provided as a pendant group along thepolymeric backbone. Pendant organoonium moieties can be chemicallyattached to the polymer backbone after polymer formation, or functionalgroups on the polymer can be converted to organoonium moieties usingknown chemistry. For example, pendant quaternary ammonium groups can beprovided on a polymeric backbone by the displacement of a “leavinggroup” functionality (such as a halogen) by a tertiary aminenucleophile. Alternatively, the organoonium group can be present on amonomer that is then polymerized or derived by the alkylation of aneutral heteroatom unit (trivalent nitrogen or phosphorous group ordivalent sulfur group) already incorporated within the polymer.

The organoonium moiety is substituted to provide a positive charge. Eachsubstituent must have at least one carbon atom that is directly attachedto the sulfur, nitrogen or phosphorus atom of the organoonium moiety.Useful substituents include, but are not limited to, substituted orunsubstituted alkyl groups having 1 to 12 carbon atoms and preferablyfrom 1 to 7 carbon atoms (such as methyl, ethyl, n-propyl, isopropyl,t-butyl, hexyl, methoxyethyl, isopropoxymethyl, substituted orunsubstituted aryl groups (phenyl, naphthyl, p-methylphenyl,m-methoxyphenyl, p-chlorophenyl, p-methylthiophenyl,p-N,N-dimethylaminophenyl, xylyl, methoxycarbonylphenyl andcyanophenyl), and substituted or unsubstituted cycloalkyl groups having5 to 8 carbon atoms in the carbocyclic ring (such as cyclopentyl,cyclohexyl, 4-methylcyclohexyl and 3-methylcyclohexyl). Other usefulsubstituents would be readily apparent to one skilled in the art, andany combination of the expressly described substituents is alsocontemplated.

The organoonium moieties include any suitable anion as described abovefor the Class I ionomers. The halides and carboxylates are preferred.

Class II ionomers can comprise both vinyl and non-vinyl backbones. Bothtypes are composed of recurring units having one or more types oforganoonium group. For example, such an ionomer can have recurring unitswith both organoammonium groups and organosulfonium groups. It is alsonot necessary that all of the organoonium groups have the same alkylsubstituents. Useful anions in these ionomers are the same as thosedescribed above for the non-vinyl polymers. Similarly, the halides andcarboxylates are preferred.

The organoonium group is present in sufficient recurring units of theionomer so that the heat-activated reaction described above can occur toprovide desired hydrophobicity of the printed image. The group can beattached along a principal backbone of the polymer, or to one or morebranches of a polymeric network, or both. Pendant groups can bechemically attached to the polymer backbone after polymer formationusing known chemistry. For example, pendant organoammonium,organophosphonium or organosulfonium groups can be provided on apolymeric backbone by the nucleophilic displacement of a pendant leavinggroup (such as a halide or sulfonate ester) on the polymeric chain by atrivalent amine, divalent sulfur or trivalent phosphorous nucleophile.Pendant onium groups can also be provided by alkylation of correspondingpendant neutral heteroatom groups (nitrogen, sulfur or phosphorous)using any commonly used alkylating agent such as alkyl sulfonate estersor alkyl halides. Alternatively a monomer precursor containing thedesired organoammonium, organophosphonium or organosulfonium group maybe polymerized to yield the desired polymer.

The organoammonium, organophosphonium or organosulfonium group in thevinyl ionomer provides the desired positive charge. Generally, preferredpendant organoonium groups can be illustrated by the followingStructures III, IV, and V:

wherein R is a substituted or unsubstituted alkylene group having 1 to12 carbon atoms that can also include one or more oxy, thio, carbonyl,amido or alkoxycarbonyl groups with the chain (such as metbylene,ethylene, isopropylene, methylenephenylene, methyleneoxymethylene,n-butylene, and hexylene), a substituted or unsubstituted arylene grouphaving 6 to 10 carbon atoms in the ring (such as phenylene, naphthylene,xylylene, and 3-methoxyphenylene), or a substituted or unsubstitutedcycloalkylene group having 5 to 10 carbon atoms in the ring (such as1,4-cyclohexylene, and 3-methyl-1,4-cyclohexylene). In addition, R canbe a combination of two or more of the defined substituted orunsubstituted alkylene, arylene and cycloalkylene groups. Preferably, Ris a substituted or unsubstituted ethyleneoxycarbonyl orphenylenemethylene group. Other useful substituents not listed hereincould include combinations of any of those groups listed above as wouldbe readily apparent to one skilled in the art.

R₃, R₄, and R₅ are independently substituted or unsubstituted alkylgroup having 1 to 12 carbon atoms (such as methyl, ethyl, n-propyl,isopropyl, t-butyl, hexyl, hydroxymethyl, methoxymethyl, benzyl,methylenecarboalkoxy, and a cyanoalkyl), a substituted or unsubstitutedaryl group having 6 to 10 carbon atoms in the carbocyclic ring (such asphenyl, napbthyl, xylyl, p-methoxyphenyl, p-methylphenyl,m-methoxyphenyl, p-chlorophenyl, p-methylthiophenyl,p-N,N-dimethylaminophenyl, methoxycarbonylphenyl, and cyanophenyl), or asubstituted or unsubstituted cycloalkyl group having 5 to 10 carbonatoms in the carbocyclic ring (such as 1,3- or 1,4-cyclohexyl).Alternatively, any two of R₃, R₄, and R₅ can be combined to form asubstituted or unsubstituted heterocyclic ring with the chargedphosphorus, sulfur or nitrogen atom, the ring having 4 to 8 carbon,nitrogen, phosphorus, sulfur or oxygen atoms in the ring. Suchheterocyclic rings include, but are not limited to, substituted orunsubstituted morpholinium, piperidinium, and pyrrolidinium groups forStructure V. Other useful substituents for these various groups would bereadily apparent to one skilled in the art, and any combinations of theexpressly described substituents are also contemplated.

Preferably, R₃, R₄, and R₅ are independently substituted orunsubstituted methyl or ethyl groups.

W⁻ is any suitable anion as described above for the Class I polymers.Acetate and chloride are preferred anions.

Ionomers containing quaternary ammonium groups as described herein aremost preferred vinyl Class II polymers.

In preferred embodiments, the vinyl Class II ionomers useful in thepractice of this invention can be represented by the following StructureVI:

wherein X′ represents recurring units to which the organoonium groups(“ORG”) are attached, Y′ represents recurring units derived fromethylenically unsaturated polymerizable monomers that may provide activesites for crosslinking using any of various crosslinking mechanisms(described below), W⁻ is a suitable anion (as defined above), and Z′represents recurring units derived from any additional ethylenicallyunsaturated polymerizable monomers. The various recurring units arepresent in suitable amounts, as represented by x′ being from about 15 toabout 99 mol %, y′ being from about 1 to about 20 mol %, and z′ beingfrom 0 to about 84 mol %. Preferably, x′ is from about 20 to about 98mol %, y′ is from about 2 to about 10 mol % and z′ is from 0 to about 70mol %.

Crosslinking of the vinyl ionomer can be achieved in the same way asdescribed above for the Class I polymers.

Additional monomers that provide the additional recurring unitsrepresented by Z′ in Structure VI include any useful hydrophilic oroleophilic ethylenically unsaturated polymerizable monomer that mayprovide desired physical or printing properties to the imaging layer.Such monomers include, but are not limited to, acrylates, methacrylates,acrylonitrile, isoprene, styrene and styrene derivatives, acrylamides,methacrylamides, acrylic or methacrylic acid and vinyl halides.

Representative Class II non-vinyl ionomers are identified herein belowas Polymers 7-8 and 10. Mixtures of these polymers can also be used.Polymer 9 is a precursor to Polymer 10. Representative vinyl ionomers ofClass II include Polymers 11-18 as identified herein below, and Polymer14 is most preferred. A mixture of any two or more of these ionomers canalso by used. Further details of such ionomers and method for preparingthem are provided in U.S. Pat. No. 6,109,830 (noted above).

Polymer 7: Poly(p-xylidenetetrahydrothiophenium chloride),

Polymer 8: Poly[phenylene sulfide-co-methyl(4-thiophenyl)sulfoniumchloride],

Polymer 9: Brominated poly(2,6-dimethyl-1,4-phenylene oxide),

Polymer 10: Dimethyl sulfonium bromide derivative ofpoly(2,6-dimethyl-1,4-phenylene oxide),

Polymer 11: Poly[methyl methacrylate-co-2-trimethylammoniumethylmethacrylic chloride-co-N-(3-aminopropyl) methacrylamide hydrochloride],

Polymer 12: Poly[methyl methacrylate-co-2-trimethylammoniumethylmethacrylic acetate-co-N-(3-aminopropyl) methacrylamide],

Polymer 13: Poly[methyl methacrylate-co-2-trimethylammoniumethylmethacrylic fluoride-co-N-(3-aminopropyl) methacrylamide hydrochloride],

Polymer 14: Poly[vinylbenzyl trimethylammoniumchloride-co-N-(3-aminopropyl) methacrylamide hydrochloride],

Polymer 15: Poly([vinylbenzyltrimethyl-phosphoniumacetate-co-N-(3-aminopropyl) methacrylamide hydrochloride],

Polymer 16: Poly [dimethyl-2-(methacryloyloxy) ethylsulfoniumchloride-co-N-(3-aminopropyl) methacrylamide hydrochloride],

Polymer 17: Poly [vinylbenzyldimethylsulfonium methylsulfate], and

Polymer 18: Poly[vinylbenzyldimethylsulfonium chloride].

Class III Ionomers

Each of the Class III ionomers has a molecular weight of at least 1000,and preferably of at least 5000. For example, the ionomers can be vinylhomopolymers or copolymers prepared from one or more ethylenicallyunsaturated polymerizable monomers that are reacted together using knownpolymerization techniques and reactants. Alternatively, they can beaddition homopolymers or copolymers (such as polyethers) prepared fromone or more heterocyclic monomers that are reacted together using knownpolymerization techniques and reactants. Additionally, they can becondensation type polymers (such as polyesters, polyimides, polyamidesor polyurethanes) prepared using known polymerization techniques andreactants. Whatever the type of polymers, at least 10 mol % (preferably15 mol %) of the total recurring units in the polymer comprise thenecessary heat-activatable thiosulfate groups.

The Class III ionomers useful in the practice of this invention can berepresented by the following Structure VII wherein the thiosulfate group(or Bunte salt) is a pendant group:

wherein A represents a polymeric backbone, R₆ is a divalent linkinggroup, and Y₁. is hydrogen or a cation.

Useful polymeric backbones include, but are not limited to, vinylpolymers, polyethers, polyimides, polyamides, polyurethanes andpolyesters. Preferably, the polymeric backbone is a vinyl polymer orpolyether.

Useful R₆ linking groups include —(COO)_(n′)(Z₁)_(m)— wherein n′ is 0 or1, m is 0 or 1, and Z₁ is a substituted or unsubstituted alkylene grouphaving 1 to 6 carbon atoms (such as methylene, ethylene, n-propylene,isopropylene, butylenes, 2-hydroxypropylene and 2-hydroxy-4-azahexylene)that can have one or more oxygen, nitrogen or sulfur atoms in the chain,a substituted or unsubstituted arylene group having 6 to 14 carbon atomsin the aromatic ring (such as phenylene, naphthalene, anthracylene andxylylene), or a substituted or unsubstituted arylenealkylene (oralkylenearylene) group having 7 to 20 carbon atoms in the chain (such asp-methylenephenylene, phenylenemethylene-phenylene, biphenylene andphenyleneisopropylenephenylene). In addition, R₆ can be an alkylenegroup, an arylene group, in an arylenealkylene group as defined abovefor Z₁.

Preferably, R₆ is an alkylene group of 1 to 3 carbon atoms, an arylenegroup of 6 carbon atoms in the aromatic ring, an arylenealkylene groupof 7 or 8 carbon atoms in the chain, or —COO(Z₁)_(m)— wherein Z₁ ismethylene, ethylene or phenylene. Most preferably, R₆ is phenylene,methylene or —COO—.

Y₁ is hydrogen, ammonium ion, or a metal ion (such as sodium, potassium,magnesium, calcium, cesium, barium, zinc or lithium ion). Preferably, Y₁is hydrogen, sodium ion, ammonium ion, or potassium ion.

As the thiosulfate group is generally arranged pendant to the backbone,preferably it is part of an ethylenically unsaturated polymerizablemonomer that can be polymerized using conventional techniques to formvinyl homopolymers of the thiosulfate-containing recurring units, orvinyl copolymers when copolymerized with one or more additionalethylenically unsaturated polymerizable monomers. Thethiosulfate-containing recurring units generally comprise at least 10mol % of all recurring units in the polymer, preferably they comprisefrom about 15 to 100 mol % of all recurring units. A polymer can includemore than one type of repeating unit containing a thiosulfate group asdescribed herein.

Ionomers having the above-described thiosulfate group are believed tocrosslink and to switch from hydrophilic thiosulfate to hydrophobicdisulfide (upon loss of sulfate) with heating.

Thiosulfate-containing molecules (or Bunte salts) can be prepared fromthe reaction between an alkyl halide and thiosulfate salt as taught byBunte, Chem.Ber. 7, 646, 1884. Polymers containing thiosulfate groupscan either be prepared from functional monomers or from preformedpolymers. Polymers can also be prepared from preformed polymers in asimilar manner as described in U.S. Pat. No. 3,706,706 (Vandenberg).Thiosulfate-containing molecules can also be prepared by reaction of analkyl epoxide with a thiosulfate salt, or between an alkyl epoxide and amolecule containing a thiosulfate moiety (such as2-aminoethanethiosulfuric acid), and the reaction can be performedeither on a monomer or polymer as illustrated by Thames, Surf Coating, 3(Waterborne Coat.), Chapter 3, pp. 125-153, Wilson et al. (Eds.).

Details for making ethylenically unsaturated polymerizable monomers andClass III ionomers are provided in U.S. Pat. No. 5,985,514 (notedabove).

Vinyl polymers can be prepared by copolymerizing monomers containing thethiosulfate functional groups with one or more other ethylenicallyunsaturated polymerizable monomers to modify polymer chemical orfunctional properties, to optimize imaging member performance, or tointroduce additional crosslinking capability.

Useful additional ethylenically unsaturated polymerizable monomersinclude, but are not limited to, acrylates (including methacrylates)such as ethyl acrylate, n-butyl acrylate, methyl methacrylate andt-butyl methacrylate, acrylamides (including methacrylamides), anacrylonitrile (including methacrylonitrile), vinyl ethers, styrenes,vinyl acetate, dienes (such as ethylene, propylene, 1,3-butadiene andisobutylene), vinyl pyridine and vinylpyrrolidone. Acrylamides,acrylates and styrenes are preferred.

Representative Class III ionomers include the following Polymers 19-27:

Polymer 19: Poly(chloromethyl-ethylene oxide-co-sodium thiosulfatemethyl-ethylene oxide),

Polymer 20: Poly(vinyl benzyl thiosulfate sodium salt-co-methylmethacylate),

Polymer 21: Poly[vinyl benzyl thiosulfate sodiumsalt-co-N-(3-aminopropyl)methacylamide hydrochloride],

Polymer 22: Poly(vinyl benzyl thiosulfate sodium salt-co-styrene),

Polymer 23: Poly(vinyl benzyl thiosulfate sodium salt),

Polymer 24: Poly[vinyl benzyl thiosulfate sodium salt-co-N-(3-aminopropyl)methacrylamide hydrochloride],

Polymer 25: Poly[2-hydroxy-3-sodium thiosulfate-propylmethacrylate-co-2-(methacryloyloxy)ethyl acetoacetate],

Polymer 26: Poly(2-sodium thiosulfate-ethyl methacrylate), and

Polymer 27: Poly(4-aza-2-hydroxy-6-sodium thiosulfatehexylmethacrylate).

Class IV Ionomers

Additional heat-sensitive ionomers useful in this invention compriserandom recurring units at least some of which comprise carboxy (freeacid) or various carboxylates (salts). The ionomers generally have amolecular weight of at least 2,000.

The ionomers randomly comprise one or more types of carboxy- orcarboxylate-containing recurring units (or equivalent anhydride units)identified as “A₁” below in Structure VIII and optionally one or moreother recurring units (non-carboxylated) denoted as “B₁” in StructureVIII.

The carboxy or carboxylate group can be linked directly to the polymerbackbone that is derived from the “A₁” monomers, or they can beconnected by a linking group identified as “X₁” in Structure VIII below.This linking group can be any divalent aliphatic, alicyclic or aromaticgroup that does not adversely affect the polymer's heat-sensitivity. Forexample, “X₁” can be a substituted or unsubstituted alkylene grouphaving 1 to 16 carbon atoms (such as methylene, ethylene, isopropylene,n-propylene and n-butylene), a substituted or unsubstituted arylenegroup having 6 to 10 carbon atoms in the arylene ring (such as m- orp-phenylene and naphthylenes), substituted or unsubstituted combinationsof alkylene and arylene groups (such arylenealkylene,arylenealkylenearylene and alkylenearylenealkylene groups), andsubstituted or unsubstituted N-containing heterocyclic groups. Any ofthese defined groups can be connected in a linking chain with one ormore amino, carbonamido, oxy, thio, amido, oxycarbonyl, aminocarbonyl,alkoxycarbonyl, alkanoyloxy, alkanoylamino, or alkaminocarbonyl groups.Particularly useful “X₁” linking groups contains an ester or amideconnected to an alkylene group or arylene group (as defined above), suchas when the ester and amide groups are directly bonded to “A₁”.

In some embodiments of Class IV polymers, the X₁ linking groups includeone or more electron withdrawing groups (groups with a positive Hammettσ_(m)) that are either within the linking chain or attached thereto.Hammett σ_(m) values are well known in the art for many chemical groupsand is defined in numerous publications including Prog. Phys. Org. Chem.2, 323, 1964, Carpenter, B. K., Determination of Organic ReactionMechanisms, John Wiley & Sons, New York, 1984, pp. 144-146, and J. Med.Chem., 16, 1207, 1973. For example, the X₁ linking groups can includeone or more of the following groups either within the linking chain orattached thereto: —O—, —S—, —Se—, —NR₁₁—, —CO—, —SO₂, —PO—, —SiR₁₁R₁₂—,—CS—, halo, cyano, —OR₁₁, —OCOR₁₁, —OCOOR₁₁, —OCONR₁₁R₁₂, —OSO₂R₁₁,—COR₁₁, —COOR₁₁, —CONR₁₁R₁₂, —NR₁₁R₁₂, —NR₁₁COR₁₂, —NR₁₁COOR₁₂,—NR₁₁CONR₁₁R₁₂, —SR₁₁, —SOR₁₁, —SO₂R₁₁, —SO₃R₁₁, and other groups thatwould be readily apparent to one skilled in the art. R₁₁ and R₁₂ areindependently any suitable organic monovalent substituent that would bereadily apparent to one skilled in the art. Preferred electronwithdrawing groups that can be a part of X₁ include —SO₂, cyano, —COR₁₁,and —SOR₁₁. Specific examples of electron withdrawing groups are alsoshown in EP-A-1,075,942 (Fuji Photo), pages 10-12, incorporated hereinby reference.

In Structure VIII below, p is 0 or 1, and preferably p is 0.

Additional monomers (non-carboxylate monomers) that provide therecurring units represented by “B₁” in Structure VIII above include anyuseful hydrophilic or oleophilic ethylenically unsaturated polymerizablecomonomers that may provide desired physical or printing properties ofprinted image or which provide crosslinkable functionalities. One ormore “B₁” monomers maybe used to provide these recurring units,including but not limited to, acrylates, methacrylates, styrene and itsderivatives, acrylamides, methacrylamides, olefins, vinyl halides, andany monomers (or precursor monomers) that do not contain carboxy orcarboxylate groups.

The carboxy- or carboxylate-containing ionomer may be chosen or derivedfrom a variety of polymers and copolymer classes including, but notnecessarily limited to polyamic acids, polyesters, polyamides,polyurethanes, silicones, proteins (such as modified gelatins),polypeptides, and polymers and copolymers based on ethylenicallyunsaturated polymerizable monomers such as acrylates, methacrylates,acrylamides, methacrylamides, vinyl ethers, vinyl esters, alkyl vinylethers, maleic acid/anhydride, itaconic acid/anhydride, styrenics,acrylonitrile, and olefins such as butadiene, isoprene, propylene, andethylene. A parent carboxy-containing polymer may contain more than onetype of carboxylic acid-containing monomer. Certain monomers, such asmaleic acid/anhydride and itaconic acid/anhydride may contain more thanone carboxylic acid unit. Preferably, the parent carboxylicacid-containing polymer is an addition polymer or copolymer containingacrylic acid, methacrylic acid, maleic acid or anhydride, or itaconicacid or anhydride or a conjugate base or hydrolysis product thereof.

In Structure VIII, n₁ represents about 25 to 100 mol % (preferably fromabout 50 to 100 mol %), and m₁ represents 0 to about 75 mol %(preferably from 0 to about 50 mol %).

While Structure VIII could be interpreted to show ionomers derived fromonly two ethylenically unsaturated polymerizable monomers, it isintended to include terpolymers and other polymers derived from morethan two monomers.

The carboxy or carboxylate groups must be present in the heat-sensitiveionomer useful in this invention in such a quantity as to provide aminimum of one mole of the carboxy or carboxylate groups per 1300 g ofpolymer and a maximum of one mole of carboxy or carboxylate groups per60 g of polymer. Preferably, this ratio (moles of carboxy or carboxylategroups to grams of polymer) is from about 1:600 to about 1:60 and morepreferably, this ratio is from about 1:500 to about 1:100. Thisparameter is readily determined from knowledge of the molecular formulaof a given ionomer.

In Structure VIII noted above, Z⁺ is any suitable monovalent cationincluding but not limited to hydrogen, alkali metal cations (such assodium or potassium), primary, secondary, tertiary, or quaternaryammonium ions, phosphonium ions, sulfonium ions, pyridinium,morpholinium, and alkyl imidazolium ions. Sodium, potassium, andquaternary ammonium ions are preferred, and quaternary ammonium ions(described below) are most preferred. The ionomer can be derived frommonomers that comprise different cations so that the ionomer chain hasvarious cations distribution throughout the molecule. Preferably, all ofthe cations are the same.

A most preferred Z⁺ cation is a quaternary ammonium ion defined as—N⁺(R₇)(R₈)(R₉)(R₁₀) in which R₇, R₈, R₉ and R₁₀ are hydrogen,independently substituted or unsubstituted alkyl groups having 1 to 12carbon atoms [such as methyl, ethyl, n-propyl, isopropyl, t-butyl,hexyl, hydroxyethyl, 2-propanonyl, ethoxycarbonymethyl, benzyl,substituted benzyl (such as 4-methoxybenzyl, o-bromobenzyl, andp-trifluoromethylbenzyl), and cyanoalkyl], or substituted orunsubstituted aryl groups having 6 to 14 carbon atoms in the carbocyclicring (such as phenyl, naphthyl, xylyl, p-methoxyphenyl, p-methylphenyl,m-methoxyphenyl, p-chlorophenyl, p-methylthiophenyl,p-N,N-dimethylaminophenyl, methoxycarbonylphenyl, and cyanophenyl).Alternatively, any two, three or four of R₇, R₈, R₉ and R₁₀ can becombined to form a ring (or two rings for four substituents) with thequaternary nitrogen atom, the ring having 5 to 14 carbon, oxygen, sulfurand nitrogen atoms in the ring. Such rings include, but are not limitedto, morpholine, piperidine, pyrrolidine, carbazole, indoline, andisoindoline rings. The nitrogen atom can also be located at the tertiaryposition of the fused ring. Other useful substituents for these variousgroups would be readily apparent to one skilled in the art, and anycombinations of the expressly described substituents are alsocontemplated.

Alternatively, multi-cationic ionic species containing more than onequaternary ammonium unit covalently bonded together and having chargesgreater than +1 (for example +2 for diammonium ions, and +3 fortriammonium ions) may be used in this invention.

Preferably, the nitrogen of the quaternary ammonium ion is directlybonded to one or more benzyl groups or one or two phenyl groups.Alternatively, the nitrogen atom is part of one or two five-memberedrings, or one or two indoline or isoindoline rings and has a molecularweight of less than 400.

The use of a spiro ammonium cation in which the nitrogen lies at thevertex of two intersecting rings is especially preferred. When acarboxylate polymer containing such an ammonium counterion is thermallyimaged, small molecule amines are not given off and hence the problem ofodor during imaging is alleviated. Similarly, the use of abenzyl-tris-hydroxyethyl ammonium ion may result in the release oftriethanolamine that is odorless and relatively benign.

The heat-sensitive ionomers of Class IV may be readily prepared usingmany methods that will be obvious to one skilled in the art. Manyquaternary ammonium salts and carboxylic acid or anhydride-containingpolymers are commercially available. Others can be readily synthesizedusing preparative techniques that would be obvious to one skilled in theart. Carboxy- or anhydride-containing polymers can be converted to thedesired quaternary ammonium carboxylate salts by a variety of methodsincluding, but not necessarily limited to:

-   -   1) the reaction of a carboxylic acid- or acid        anhydride-containing polymer with the hydroxide salt of the        desired quaternary ammonium ion,    -   2) the use of ion exchange resin containing the desired        quaternary ammonium ion,    -   3) the addition of the desired ammonium ion to a solution of the        carboxylic acid-containing polymer or a salt thereof followed by        dialysis,    -   4) the addition of a volatile acid salt of the desired        quaternary ammonium ion (such as an acetate or formate salt) to        the carboxylic acid-containing polymer followed by evaporation        of the volatile component upon drying,    -   5) electrochemical ion exchange techniques,    -   6) the polymerization of monomers containing the desired        quaternary ammonium carboxylate units, and    -   7) the combination of a specific salt of the carboxylic        acid-containing polymer and a specific quaternary ammonium salt,        both chosen such that the undesired counterions will form an        insoluble ionic compound in a chosen solvent and precipitate.

Preferably, the first method is employed.

Although it is especially preferred that all of the carboxy (or latentcarboxylic acid) functionalities of the ionomer are converted to thedesired salts (especially quaternary ammonium salts), imagingcompositions in which the ionomer is incompletely converted may stillretain satisfactory imageability. Preferably, at least 50 monomerpercent of the carboxylic acid (or equivalent anhydride) containingmonomers are reacted to form the desired carboxylates.

Preferred embodiments of Class IV ionomers are crosslinked. Crosslinkingcan be provided in a number of ways as described above for the Class Iionomers. Ethylenically unsaturated polymerizable monomers havingcrosslinkable groups (or groups that can serve as attachment points forcrosslinking additives) can be copolymerized with the other monomers asnoted above. Such monomers include, but are not limited to,3-(trimethylsilyl)propyl acryl ate or methacrylate, cinnamoyl acryl ateor methacrylate, N-methoxymethyl methacrylamide,N-aminopropylmethacrylamide hydrochloride, acrylic or methacrylic acidand hydroxyethyl methacrylate.

Preferably, crosslinking is provided by the addition of anepoxy-containing resin to a quaternary ammonium carboxylate ionomer orby the reaction of a bisvinylsulfonyl compound with amine containingunits (such as N-aminopropylmethacrylamide) within the ionomer. CR-5L(an epoxide resin sold by Esprit Chemicals) can be used for thispurpose.

In still more preferred embodiments of Class IV ionomers, the quaternaryammonium counterion of the carboxylate functionalities may be anyammonium ion in which the nitrogen is covalently bound to a total offour alkyl or aryl substituents as defined above, provided at least oneof the four substituents is a substituted alkylene(C₁-C₃)phenyl group.

More particularly in such embodiments, in Structure VIII noted above, Z⁺is a quaternary ammonium ion in which R₇, R₈ and R₉ are independentlylinear or branched unsubstituted alkyl groups of 1 to 3 carbon atoms, orlinear or branched hydroxyalkyl groups of 1 to 3 carbon atoms thatcomprise 1 to 3 hydroxy groups as the only substituents (generally onlyone hydroxy group per carbon atom). More preferably, these radicals areindependently methyl, hydroxymethyl, ethyl, 2-hydroxyethyl,1-hydroxyethyl, or 1,2-dihydroxyethyl and most preferably, they areeither methyl or 2-hydroxyethyl.

In this group of preferred Class IV ionomers, R₁₀ is a substitutedalkylenephenyl group that has at least one substituent on either thealkylene or phenyl moiety of the group. More preferably, the one or moresubstituents are on the phenyl moiety. The alkylene moiety can be linearor branched in nature and has from 1 to 3 carbon atoms (such asmethylene, ethylene, n-propylene or isopropylene). Preferably, thealkylene moiety of R₁₀ has 1 or 2 carbon atoms and more preferably, itis methylene. The alkylene moiety can have as many substituents as thereare available hydrogen atoms to be removed from a carbon atom. Usefulalkylene substituents are the same as those described below in definingthe phenyl substituents, but the most preferred substituents for thealkylene moiety are fluoro and alkoxy.

The phenyl moiety of R₁₀ can have from 1 to 5 substituents in any usefulsubstitution pattern. Useful substituents include but are not limitedto, halo groups (such as fluoro, chloro, bromo, and iodo), substitutedor unsubstituted alkyl groups having from 1 to 12 carbon atoms (such asmethyl, ethyl, isopropyl, t-butyl, n-pentyl and n-propyl) that can befurther substituted with any of the substituents listed herein (such ashaloalkyl groups including trihalomethyl groups), substituted orunsubstituted alkoxy groups having 1 to 12 carbon atoms (such asmethoxy, ethoxy, isopropoxy, n-pentoxy and n-propoxy), cyano, nitro,substituted or unsubstituted aryl groups having 6 to 14 carbon atoms inthe aromatic carbocyclic ring (as defined above for R₇, R₈ and R₉),substituted or unsubstituted alkyleneoxycarbonyl groups having 2 to 12carbon atoms (such as methyleneoxycarbonyl, ethyleneoxycarbonyl andi-propyleneoxycarbonyl), substituted or unsubstituted alkylcarbonyloxygroups having 2 to 12 carbon atoms (such as methylenecarbonyloxy,ethylenecarbonyloxy and isopropylenecarbonyloxy), substituted orunsubstituted alkylcarbonyl groups having 2 to 12 carbon atoms (such asmethylenecarbonyl, ethylenecarbonyl and isopropylenecarbonyl), amidogroups, aminocarbonyl groups, trihalomethyl groups, perfluoroalkylgroups, formyl, mercapto and substituted or unsubstituted heterocyclicgroups having 5 to 14 atoms in the ring that includes one or morenitrogen, sulfur, oxygen or selenium atoms with the remainder beingcarbon atoms (such as pyridyl, oxazolyl, thiphenyl, imidazolyl, andpiperidinyl).

Preferably, R₁₀ contains 1 to 5 substituents (more preferably 1 or 2substituents) on the phenyl moiety, which substituents are either halogroups, substituted or unsubstituted methyl or ethyl groups, orsubstituted or unsubstituted methoxy or 2-ethoxy groups. Morepreferably, R₁₀ comprises 1 to 3 methyl, fluoro, chloro, bromo ormethoxy groups, or any combination of these groups on either thealkylene or phenyl moiety.

Representative preferred ionomers of Class IV include the followingPolymers 28-36:

Additional preferred ionomers of Class IV include the following Polymers37-50 wherein R₁₀ includes a substituted alkylenephenyl group:

The inkjet ink of the present invention can include one or more Class I,II, III, or IV ionomers with or without minor amounts of additionalbinder or polymeric materials that will not adversely affect itsproperties. The heated sensitive ionomers employed in the invention ingeneral is present in the ink jet ink generally from 0.1% to 20% byweight, preferably from 0.5% to 10% by weight. When use as a binder, theweight ratio of the pigment to the polymer is 1:20 to 20:1, preferably1:5 to 3:1.

The heat-sensitive ionomer can be water soluble or water dispersible. Ifthe heat-sensitive ionomer is water dispersible, the particle size ofthe dispersion is less than 1 micron, preferably less than 0.5 micron.

The aqueous carrier medium for the ink composition is water or a mixtureof water and at least one water miscible co-solvent. Selection of asuitable mixture depends on requirements of the specific application,such as desired surface tension and viscosity, the selected pigment,drying time of the pigmented ink jet ink, and the type of substrateronto which the ink will be printed. Representative examples ofwater-miscible co-solvents that may be selected include (1) alcohols,such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropylalcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, iso-butylalcohol, furfuryl alcohol, and tetrahydrofurfuryl alcohol; (2) ketonesor ketoalcohols such as acetone, methyl ethyl ketone and diacetonealcohol; (3) ethers, such as tetrahydrofuran and dioxane; (4) esters,such as ethyl acetate, ethyl lactate, ethylene carbonate and propylenecarbonate; (5) polyhydric alcohols, such as ethylene glycol, diethyleneglycol, triethylene glycol, tetraethylene glycol, propylene glycol,polyethylene glycol, glycerol, 2-methyl-2,4-pentanediol1,2,6-hexanetriol and thioglycol; (6) lower alkyl mono- or di-ethersderived from alkylene glycols, such as ethylene glycol mono-methyl (or-ethyl) ether, diethylene glycol mono-methyl (or -ethyl) ether,diethylene glycol mono-butyl (or -ethyl) ether, propylene glycolmono-methyl (or -ethyl) ether, poly(ethylene glycol) butyl ether,triethylene glycol mono-methyl (or -ethyl) ether and diethylene glycoldi-methyl (or -ethyl) ether; (7) nitrogen containing cyclic compounds,such as pyrrolidone, N-methyl-2-pyrrolidone, and1,3-dimethyl-2-imidazolidinone; and (8) sulfur-containing compounds suchas dimethyl sulfoxide, 2,2′-thiodiethanol, and tetramethylene sulfone.

The amount of aqueous carrier medium is in the range of approximately 70to 99 weight %, preferably approximately 90 to 98 weight %, based on thetotal weight of the ink. A mixture of water and a polyhydric alcohol,such as diethylene glycol, is useful as the aqueous carrier medium. In apreferred embodiment, the inks contain from about 5 to about 80%, morepreferably 20-60% by weight of water miscible organic solvent based onthe total weight of the aqueous carrier medium.

Jet velocity, separation length of the droplets, drop size and streamstability are greatly affected by the surface tension and the viscosityof the ink. The ink jet inks suitable for use with ink jet printingsystems and to apply to non-absorbing substrates, especially highsurface energy hydrophobic surfaces, should have a surface tension inthe range of about 20 dynes/cm to about 60 dynes/cm and, morepreferably, in the range 20 dynes/cm to about 35 dynes/cm. Control ofsurface tensions in aqueous inks is accomplished by additions of smallamounts of surfactants. The level of surfactants to be used can bedetermined through simple trial and error experiments, usually about0.1% to about 6%, preferably, 0.5% to about 4% by weight of the totalink composition. Anionic, cationic and nonionic surfactants may beselected from those disclosed in U.S. Pat. Nos. 5,324,349; 4,156,616 and5,279,654 as well as many other surfactants known in the ink jet inkart. Commercial surfactants include the Surfynols® from Air Products;the Zonyls® from DuPont and the Fluorads® from 3M. Preferred surfactantscan be silicon surfactants or fluorinated surfactants. Preferred siliconsurfactants are available from BYK-Chemie as BYK surfactants, and fromCrompton Corp, as Silwet® surfactants. Commercially availablefluorinated surfactants can be the Zonyls® from DuPont and the Fluorads®from 3M, they can be used alone or in combination with othersurfactants.

A humectant is added to the composition employed in the process of theinvention to help prevent the ink from drying out or crusting in theorifices of the ink jet printhead. Polyhydric alcohols useful in thecomposition employed in the invention for this purpose include, forexample, ethylene glycol, diethylene glycol, triethylene glycol,propylene glycol, tetraethylene glycol, polyethylene glycol, glycerol,2-methyl-2,4-pentanediol, 1,2,6-hexanetriol and thioglycol. Thehumectant may be employed in a concentration of from about 10 to about50% by weight of the entire ink composition. In a preferred embodiment,diethylene glycol or a mixture of glycols is employed a concentration ofbetween 10 and 20% by weight of the entire ink composition.

A penetrant or ink solvent (0-10% by weight) may also be added to theink composition employed in the process of the invention to help the inkpenetrate the receiving substrate, especially when the substrate is ahighly non-absorbing. A preferred penetrant for the inks employed in thepresent invention is n-propanol at a final concentration of 1-6% byweight. The type of humectant or ink solvent was chosen based on theevaporation rate and the effectiveness of interaction with the substratesuch as untreated vinyl. The preferred humectants are polyhydricalcohols that has an boiling point of 200° C. or less, more preferably150° C. or less.

The ink has physical properties compatible with a wide range of ejectingconditions, i.e., driving voltages and pulse widths for thermal ink jetprinting devices, driving frequencies of the piezo element for either adrop-on-demand device or a continuous device, and the shape and size ofthe nozzle.

A penetrant (0-10% by weight) may also be added to the ink compositionemployed in the process of the invention to help the ink penetrate thereceiving substrate, especially when the substrate is a highly sizedpaper. A preferred penetrant for the inks employed in the presentinvention is n-propanol at a final concentration of 1-6% by weight.

A biocide (0.01-1.0% by weight) may also be added to prevent unwantedmicrobial growth which may occur in the ink over time. A preferredbiocide for the inks employed in the present invention is Proxel® GXL(Zeneca Colours Co.) at a concentration of 0.05-0.5% by weight.Additional additives which may optionally be present in ink jet inksinclude thickeners, conductivity enhancing agents, anti-kogation agents,pH buffering agents, drying agents, and defoamers.

Ink jet inks made using polymers employed in this invention are employedin ink jet printing wherein liquid ink drops are applied in a controlledfashion to an ink receiving substrate, by ejecting ink droplets fromplurality of nozzles, or orifices, in a print head of ink jet printers.

Commercially available ink jet printers use several different methods tocontrol the deposition of the ink droplets. Such methods are generallyof two types: continuous stream and drop-on-demand.

In drop-on-demand systems, a droplet of ink is ejected from an orificedirectly to a position on the ink receiving layer by pressure createdby, for example, a piezoelectric device, an acoustic device, or athermal process controlled in accordance digital data signals. An inkdroplet is not generated and ejected through the orifices of the printhead unless it is needed. Ink jet printing methods, and relatedprinters, are commercially available and need not be described indetail.

To accelerate the printing speed and increase durability, an in-situheating step during printing and a post heating step are preferred.Heating will allow fluid not only to spread on the non-absorbingsubstrate but also to evaporate faster, and help the ink componentinteraction with the non-absorbing substrate by swelling or penetratingmechanism. The in-situ heating step can be achieved using a heatingmeans such that the non-absorbing substrate is heated to elevatedtemperature during the printing. The temperature range of substrate ispreferably between 30° C. and 90° C., more preferably between 40 and 70°C. A post-heating step after printing is further preferred. During thepost heating, the printed substrate is heated to elevated temperatureusing a heating means where the temperature range of the substrate ispreferably between 50° C. and 150° C., more preferably between 80 and120° C. Various methods may be used for the means of heating, forexample, light irradiation, a hot air source or an electrical heater.For in-situ heating, the electrical heater is preferred. Forpost-heating, light irradiation such as using an infrared lamp ispreferred. Optionally, an infrared absorbing material can be employed inthe ink of the present invention to assist the heating by infrared lamp.

The following examples illustrate the utility of the present invention.

EXAMPLES

Preparation of Polymer Dispersions

Preparation of Comparative Polymer Dispersion 1 (PC-1: Acrylate Non-HeatSensitive)

600 g of deionized water and 3.6 g Triton 770® surfactant were chargedto a 1-liter, three-neck round-bottom flask equipped with a mechanicalstirrer and nitrogen inlet. The solution was purged with nitrogen for 30min and heated to 60° C. in a constant temperature bath. 36.0 g ofstyrene, 90.0 g of butyl methacrylate and 54.0 g of methacrylic acidwere added and stirred for three minutes. 16.4 g of 10% sodiumpersulfate solution and 5.5 g of 10% sodium metabisulfite solution wereadded to initiate the polymerization. Polymerization was continued forone hour and heated one more hour at 60° C. The temperature was reducedto 50° C. and 1 ml each of t-butyl hydroperoxide (10%) and sodiumformaldehyde bisulfite (10%) were post-added. The content of thehydrophilic monomer is 30% by weight of the total polymer. The latex wascooled and filtered. The dispersion contains 22.2% solid by weight.

Preparation of Comparative Polymer Dispersion 2 (PC-2: Water SolubleAcrylate, Non-Heat Sensitive)

Commercially available alkaline soluble resin Trudot IJ-4655® isobtained from Westvaco as a 100% net solid. 25.0 g of Trudot IJ-4655 wasmixed with 5.8 g KOH and 69.2 g distilled water. The mixture was stirredat room temperature for 48 hours. The resulted solution was filteredthrough a 3 micron filter. The final solution contains 25.0% solids.

Preparation of Comparative Polymer Dispersion 3 (PC-3: HydrophobicPolymer, Non-Heat Sensitive)

160 g deionized water were charged to a 500 mL 1-neck round bottom flaskequipped with mechanical stirrer. The flask was first flushed withnitrogen for 20 minutes, then immersed in a constant temperature bath at40° C. Afterwards, 0.25 g of potassium persulfate, 0.35 g sodiummetabisufite, 2.0 g Triton 770 (30% active), 4.0 g of ethyl acrylate,36.0 g vinylidene chloride were added to the flask. The polymerizationreaction was continued for additional 12 hours. The latex was cooled andfiltered. The final polymer latex dispersion contained 13.52% solid byweight and the average particle size is 0.056 micron. This polymercontains no hydrophilic monomer. This polymer dispersion is designatedas Comparative Polymer Dispersion 3 (PC-3).

Preparation of Heat-Sensitive Ionomer 1 of the Invention P-1 (Class III,Thiosulfate Ionomer)

A five-liter three-neck flask was equipped with a mechanical stirrer, anargon bleed and a condenser. The vessel was placed in a heatingapparatus and the stirrer set to 100 rpm. With stirring, 120 mL ofdemineralized water was added to the vessel, followed by 118.6 g (0.75mol) of sodium thiosulfate. The sodium thiosulfate was stirred untilcompletely dissolved at room temperature. To this clear solution wasadded 111.4 g (0.73 mol) chloromethylstyrene (a mixture of 3- and4-chloromethylstyrene), followed by 360 g of methanol. The mixture washeated to a gentle reflux temperature of around 70 C., under a slightargon flow, and stirred at this temperature for 3 hours. The solutionwas allowed to cool slowly to room temperature and 1720 g of methanolwas added, followed by 365 g (3.65 mol) of methyl methacrylate. Thesolution was heated to 60 C., and 2.5 g (0.45 wt % of monomers)2,2′-azobis(2-methylpropanenitrile) (Vazo 64) was added. The solutionwas heated to a gentle reflux at around 70 C., under positive argonpressure, and stirred for 24 hours. The polymer product was cooled toroom temperature, filtered through course cloth, and ultrafiltered toremove residual small molecules. The final aqueous product was hazy,3260 g at 13.8% solid, 82% yield. Molecular weight average bySEC=149,000.

Preparation of Heat Sensitive Ionomer 2 of the Invention P-2: (Class IV,Ammonium Salt Ionomer)

Commercially available alkaline soluble resin Trudot IJ-4655® isobtained from Westvaco as a 100% net solid. 25.0 g of Trudot IJ-4655 wasmixed with 6.07 g ammonium hydroxide solution (29% active) and 68.9 gdistilled water. The mixture was stirred at room temperature for 48hours. The resulted clear solution was filtered through a 3 micronfilter. The final solution contains 26.28% solids.

Preparation of Pigment Dispersion

The magenta pigment dispersion contains: 300 g of Polymeric beads, meandiameter of 50 μm (milling media); 30 g of quinacridone magenta pigmentPigment Red 122 (Sun Chemicals); 9 g of Oleoyl methyl taurine, (OMT)Potassium salt and 208 g of Deionized water, and 0.2 g of Proxel GXL®(biocide from Zeneca). The above components were milled in a 2 literdouble walled vessel obtained from BYK-Gardner using a high energy mediamill manufactured by Morehouse-Cowles Hochmeyer. The mill was run forapproximately 8 hours at room temperature. The dispersion was separatedfrom the milling media by filtering the millgrind through a 4-8 μmKIMAX® Buchner Funnel obtained from VWR Scientific Products. At the endof milling, additional water is added to the dispersion so that thepigment is about 10.0% by weight of the total final dispersion and thebiocide is about 230 ppm by weight of the total final dispersion. Theparticle size is about 30 nm as measured by MICROTRAC II Ultrafineparticle analyzer (UPA) manufactured by Leeds & Northrup.

Ink Formulation

Ink 1 of the Invention (I-1) (P-1 as a Binder)

To prepare the Ink-1, 4.36 g of the Magenta Pigment Dispersion (10%active), 0.2 g Silwet® L-7608 (Crompton Corp.), 2.0 g triethylene glycoland 1.0 g di(propyleneglycol) methyl ether (Dowanol® DPM), 0.6 g2-pyrrolidone, and 2.84 g of Polymer Dispersion P-1 (13.80% active) wereadded together with distilled water so that the final weight of the inkwas 20.0 g. The final ink contained 2.18% Pigment Red 122, 1.0% Silwet®L-7608, 10.0% diethylene glycol, 5% di(propyleneglycol) methyl ether, 3%2-pyrrolidone and 1.96% Polymer Dispersion P-1. The solution wasfiltered through a 3 μm polytetrafluoroethylene filter.

Ink 2 of the Invention (I-2) (P-2 as a Binder)

Ink-2 of the present invention was prepared similar to Ink-1 except that1.49 g of Polymer Dispersion P-2 (26.28% active) was used instead ofPolymer Dispersion 2 such that the final ink contained 1.96% of PolymerDispersion P-2 by weight of the total ink.

Comparative Ink 1 (C-1: Acrylic Latex, Non-Heat Sensitive)

The comparative ink 1 was prepared similar to Ink-1 of the Inventionexcept that 1.76 g of Comparative Polymer Dispersion PC-1 (22.2% active)was used instead of Polymer Dispersion 1. The final Ink contained 1.96%of Comparative Polymer Dispersion PC-1.

Comparative Ink 2 (C-2: Water Soluble Polymer, Non-Heat Sensitive)

The comparative ink 2 was prepared similar to Comparative Ink 1 exceptthat 1.57 g of Comparative Polymer Dispersion PC-2 (25% active) was usedinstead of Polymer Dispersion 1. The final Ink contained 1.96% ofComparative Polymer Dispersion PC-2.

Comparative Ink 3 (C-3: Hydrophobic Polymer, Non-Heat Sensitive)

The comparative ink 2 was prepared similar to Comparative Ink 1 exceptthat 2.96 g of Comparative Polymer Dispersion PC-3 (13.25% active) wasused instead of Polymer Dispersion 1. The final Ink contained 1.96% ofComparative Polymer Dispersion PC-3.

Ink Firability Test

The Inks of present invention were filled into Epson 880 emptycartridges and printing was done with an Epson 880 Ink jet printer,using the above inks. All inks of the invention fired well through theEpson 880 printer, no nozzles were clogged. The inks were left inprinter for over 48 hours and the above printing test was repeated. Theinks are rated as following:

A: All the nozzles were firing with minimum cleaning cycles without anyproblems for the inks of the present invention.

B: Some nozzles were missing after at least three cleaning cycles.

C: A lot of nozzles were missing after extensive cleaning (>3 cleaningcycles)

D: Didn't fire at all.

The tested results are listed in Table 1

Durability Test

Test Sample Preparation

A non-absorbing vinyl substrate, a multi-purpose inkjet cast vinyl (MPI1005 #226 from Avery Graphics) was cut into 14 by 25 cm in size andplaced on a heated coating block with temperature at about 40° C. Theabove inks were filled into an airbrush (Paasche Sirbrush Set H-3available from Paasche Airbrush Company, Harwood Heights, Ill.)connected to compressed house air. The pressure of the airbrush wasadjusted to about 7.46 Kg such that smooth ink flow was obtained. Theinks were sprayed onto the heated vinyl substrates described above.Uniform coatings of the inks were obtained. The selected samples werethen heated at 90° C. for 1 minute using an infrared lamp.

Dry Rub Resistance Test

The dry rub resistance test was carried out by rubbing the samples witha dry Q-tip for 4 passes under a consistent pressure in the inked area.The color loss in the treated sample area and the color transfer toQ-tip were examined visually and a rating of the dry rub resistance wasgiven as follows on a scale of 0 to 5.

0: Best. No color loss, and/or color transfer;

1: hardly visible amount of color loss and/or color transfer;

2: visible amount of color loss and/or color transfer;

3: some color loss and color transfer;

4: large amount of color loss and color transfer;

5: Worst. Almost complete color loss and color transfer.

Wet Rub Resistance Test

A wet rub resistance test was carried out by placing an approximately2.54 cm diameter water droplet on the ink-coated sample surface for 5minutes, after which the excess water was wiped off with a paper towel.The above treated area was then rubbed with a dry paper towel for 4passes under a consistent pressure a 3.5 cm diameter area. The colorloss in the treated sample area and the color transfer to the papertowel were examined visually and a rating of the wet rub resistance wasgiven similar as above on a scale of 0 to 5, 0 being the best and 5being the worst. Both of the dry and wet rub resistance test results areshown in Table 1.

TABLE 1 Polymer Firability Dry Rub Wet Rub Ink Binder Rating RatingRating C-1 PC-1 B 2 4 C-2 PC-2 A 1 4 C-3 PC-3 C 0 1 I-1 P-1 A 0 1 I-2P-2 A 1 1

From the above table, it is evident that the presence of heat sensitiveionomer in the ink significantly improves both the ink firability aswell as image durability in comparison with the comparative inks.

1. An aqueous inkjet ink composition comprising: a pigment; a watersoluble heat-sensitive ionomer, at least one surfactant; a humectant;wherein the ionomer is a charged polymer having at least 15 mole % ofthe recurring units negatively or positively charged.
 2. The compositionof claim 1 wherein the heat-sensitive ionomer is selected from thefollowing four classes of polymers: I) a crosslinked or uncrosslinkedvinyl polymer having recurring units comprising positively-charged,pendant N-alkylated aromatic heterocyclic groups; II) a crosslinked oruncrosslinked polymer having recurring organoonium groups; III) apolymer comprising a pendant thiosulfate group; and IV) a polymercomprising recurring units having carboxy or carboxylate groups.
 3. Thecomposition of claim 2 wherein said heat-sensitive ionomer falls withinClass I polymer and is represented by the Structure I:

wherein R₁ is an alkyl group, R₂ is an alkyl group, an alkoxy group, anaryl group, an alkenyl group, halo, a cycloalkyl group, or aheterocyclic group having 5 to 8 atoms in the ring, Z″ represents thecarbon and nitrogen, oxygen, or sulfur atoms necessary to complete anaromatic N-heterocyclic ring having 5 to 10 heteroatoms in the ring, nis 0 to 6, and W⁻ is an anion.
 4. The composition of claim 3 wherein R₁is an alkyl group of 1 to 6 carbon atoms, R₂ is a methyl, ethyl orn-propyl group, Z″ represents the carbon, nitrogen, oxygen, and sulfuratoms to complete a 5-membered ring, and n is 0 or
 1. 5. The compositionof claim 2 wherein said heat-sensitive ionomer falls under Class IIpolymer in claim 2 and is a polyester, polyamide, polyamide-ester,polyarylene oxide or a derivative thereof, polyurethane, polyxylylene ora derivative thereof, a poly(phenylene sulfide) ionomer, or asilicon-based sol gel.
 6. The composition of claim 2 wherein saidionomer falls under Class II polymer and comprises an organoonium moietythat is a pendant quaternary ammonium group on the backbone of saidClass II polymer.
 7. The composition of claim 2 wherein saidheat-sensitive ionomer falls under Class II vinyl polymer represented byeither of Structures III, IV or V:

wherein R is an alkylene, arylene, or cycloalkylene group or acombination of two or more such groups, R₃, R₄ and R₅ are independentlysubstituted or unsubstituted alkyl, aryl or cycloalkyl groups, or anytwo of R₃, R₄ and R₅ can be combined to form a heterocyclic ring withthe charged phosphorus, nitrogen or sulfur atom, and W⁻ is an anion. 8.The composition of claim 7 wherein R is an ethyleneoxycarbonyl orphenylenemethylene group, and R₃, R₄ and R₅ are independently a methylor ethyl group, and W⁻ is a halide or carboxylate.
 9. The composition ofclaim 8 wherein x′ is from about 20 to about 98 mol %, y′ is from about2 to about 10 mol % and z′ is from 0 to about 73 mol %.
 10. Thecomposition of claim 7 represented by the structure VI:

wherein ORG represents organoonium groups, X′ represents recurring unitsto which the ORG groups are attached, Y′ represents recurring unitsderived from ethylenically unsaturated polymerizable monomers that mayprovide active sites for crosslinking, Z′ represents recurring unitsderived from any additional ethylenically unsaturated polymerizablemonomers, w+ is an anion, x′ is from about 15 to about 99 mol %, y′ isfrom about 1 to about 20 mol %, and z′ is from 0 to about 84 mol %. 11.The composition of claim 2 wherein said heat-sensitive ionomer fallsunder Class IV polymer and comprises at least 1 mole of carboxy orcarboxylate groups per 1300 g of polymer.
 12. The composition of claim11 wherein said heat-sensitive ionomer is represented by Structure VIIIbelow wherein “A₁” represents recurring units derived from ethylenicallyunsaturated polymerizable monomers, X₁ is a divalent linking group, Z⁺ amonovalent cation, and B₁ represents non-carboxylated recurring units, pis 0 or 1, m₁ is 0 to about 95 mol %, and n₁ is from about 5 to 100 mol%.


13. The composition of claim 1 wherein said heat-sensitive ionomer fallsunder Class I polymer in claim 2 and it is represented by the StructureII:

wherein HET⁺ represents a positively-charged, pendant N-alkylatedaromatic heterocyclic group, X represents recurring units havingattached HET⁺ groups, Y represents recurring units derived fromethylenically unsaturated polymerizable monomers that provide activecrosslinking sites, Z represents recurring units for additionalethylenically unsaturated monomers, x is from about 15 to 100 mol %, yis from 0 to about 20 mol %, z is from 0 to about 85 mol %, and W⁻ is ananion.
 14. The composition of claim 13 wherein said positively-charged,pendant N-alkylated aromatic heterocyclic group is an imidazolium orpyridinium group.
 15. The composition of claim 1 wherein saidheat-sensitive ionomer falls under Class III polymer in claim 2 and is apolymer having the Structure VII:

wherein A represents a polymeric backbone, R₆ is a divalent linkinggroup, and Y₁ is a hydrogen or a cation.
 16. The composition of claim 15wherein R₆ is an alkylene group, an arylene group, an arylenealkylenegroup, or —(COO)_(n′)(Z₁)_(m) wherein n′ is 0 or 1, and Z₁ is analkylene group, an arylene group, or an arylenealkylene group, and Y₁ ishydrogen, ammonium ion or a metal ion.
 17. The composition of claim 16wherein R₆ is an alkylene group of 1 to 3 carbon atoms, an arylene of 6carbon atoms in the aromatic ring, an arylenealkylene of 7 or 8 carbonatoms in the chain, or —COOZ₁ wherein Z₁ is methylene, ethylene orphenylene, and Y₁ is hydrogen, ammonium, sodium, or potassium.
 18. Thecomposition of claim 1 wherein said heat-sensitive ionomer has a meanparticle size of less than 1 micron.
 19. The composition of claim 1wherein said heat-sensitive ionomer has a mean particle size of lessthan 0.5 micron.
 20. The composition of claim 1 wherein the weight ratioof the pigment to the polymer is 1:20 to 20:1.
 21. The composition ofclaim 1 wherein the weight ratio of the colorant to the polymer is 1:5to 3:1.
 22. The ink composition of claim 1 wherein the pigment particlescomprise up to 10% by weight of the ink composition.
 23. The inkcomposition of claim 1 wherein the said surfactant is a siliconated or afluorinated surfactant or a mixture of both.
 24. The composition ofclaim 1 wherein the said pigment is a self-dispersing pigment, anencapsulated pigment or a pigment dispersed by a dispersant.
 25. Anaqueous inkjet ink and receiver combination wherein said aqueous ink jetink comprises: a pigment; a heat sensitive ionomer; at least onesurfactant; a humectant; and said receiver comprises a non-absorbingsubstrate.
 26. The combination of claim 25 wherein the non-absorbingsubstrate is a plastic, glass, ceramic or metal substrate.
 27. Thecombination of claim 28 wherein said plastic substrate is an untreatedvinyl.